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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



ject to physical laws and an efferent component result- 

 ing in a muscular movement. All reactions, however 

 they might be described in common parlance as 

 pleasure, fear, distress or other descriptive terms were, 

 according to him, in essence muscular in expression. 

 During the passage of the inflow through the central 

 portion of the arc there could either be excitation 

 which would augment the reflex motor response (as 

 in so-called emotional states) or inhibition which 

 would decrease the reflex muscular movement, the 

 resultant beine; 'rational' controlled behavior. It is 

 interesting that Sechenov conceived that inhibition 

 could be learned and that with maturity an increase 

 in the degree of inhibition exerted was achieved. 



Thus, according to Sechenov, all human behavior 

 was a balance between inhibition and excitation 

 operating mechanically at the central link of the re- 

 flex arc. A so-called 'willed' movement according to 

 him only apparently lacked the first component of the 

 arc, its afferent inflow being material memory traces 

 left by external stimuli in the past. It was in elaborat- 

 ing this part of his theory that Sechenov approached 

 the concept of the conditional reflex, for he postulated 

 that the memory trace of a past sensory experience 

 could be evoked by the recurrence of any fraction of 

 it even if this fraction were quite insignificant and 

 unrelated in its apparent meaning. This is essentially 

 the principle underlying the formulation of the condi- 

 tional reflex theory, namely the potency of an indiffer- 

 ent external stimulus provided it is repeatedly time- 

 locked to the original experience. One further point 

 should be noted in this early attempt to relate mental 

 processes to brain physiology. Sechenov believed that 

 man had the special faculty of increasing the degree 

 of inhibition exerted at the central link until a level 

 of total inhibition of the efferent discharge was 

 reached, and he held that thought was an example of 

 this condition. 



Although terms such as 'cerebral reflexes' and 

 'psychical reflexes' abound in the nineteenth century 

 literature, they were mostly used by psychologists 

 to describe automatisms. At this period only a few 

 writers had broached the problem of explaining 

 mental processes in physiological terms. Thomas Lay- 

 cock C312), whose belief in cortical localization no 

 doubt influenced his pupil Hughlings Jackson, wrote 

 in 1845 a paper On the reflex function of the brain. In this 

 he stated his belief that "the brain although the organ 

 of consciousness, was subject to the laws of reflex ac- 

 tion, and that in this respect it did not differ from other 



312. Laycock, Thomas (1812-1876). On the reflex function 

 of the brain. Brit. & For. Med. Rev. 19: 298, 1845. 



ganglia of the nervous system." He too envisaged a 

 three-component arc, the central link in the brain 

 being one where 'ideagenous' changes took place that 

 influenced the motor output. He came close to antic- 

 ipating one of Sechenov's postulates by stating that 

 the actual sensory impression of an object or the mere 

 idea of it could evoke the same 'ideagenous' change 

 in the brain and result in a similar reflex motor effect. 

 So firmly did Laycock believe in the neuronal basis 

 of ideas that he calculated how many there could be 

 to the square inch of grey matter (the answer was 

 8000) and argued that "as there must be an immense 

 number of square inches of surface in the grey matter 

 extended through the cerebrospinal axis of man, there 

 is space sufficient for millions." We find echoes of this 

 kind of calculation in some of today's conjectures 

 about the number of possible interconnections in the 

 brain. 



Laycock did not test his hypotheses by experiment 

 though he argued from a basis of clinical observation, 

 for he said "an experiment is occasionally made by 

 nature." There is no evidence that Sechenov was 

 aware of Laycock's ideas, although he was influenced 

 by the writings of two other nonexperimentalists, 

 Herbert Spencer (313) and George Henry Lewes 

 (314). These two men, united through their relation- 

 ships with George Eliot, were influential not only on 

 Sechenov but on Pavlov. Their writings, now largely 

 unread, were translated into Russian almost immedi- 

 ately after publication and were everywhere highly 

 regarded. .Spencer's work was an argument for cortical 

 representation of mental function, and Hughlings 

 Jackson was one who expressed indebtedness to him. 

 Spencer based much of his argument on comparative 

 evolution though he was writing 4 years before the 

 publication of the Origin of the Species by Darwin 

 (315), another writer whose books were extremely 

 influential on Ru.ssian thought. Spencer stressed 

 localization of mental processes, saying that "whoever 

 calmly considers the question cannot long resist the 

 conviction that different parts of the brain must in 

 some way or other suhserve different kinds of mental 

 action." When we find in his Autobiography (316) that 



313. Spencer, Herbert (1820-1903). Principles of Psychology. 

 1855. 2 vol. 



314. Lewes, George Henry (18 17-1 878). The Physiology of the 

 Common Life. London: Blackwood, 1859. 2 \'ol. 



315. Darwin, Charles Robert (1809-1882). On the Origin of 

 Species by means of .Kaiural Selection or the Preservation of 

 Favoured Races in the Struggle for Life. London: John 

 Murray, 1859. 



316. Spencer, H. .In Autobiography. London: Williams & 

 Norgate, 1904. 2 vol. 



